Absolute zero The theoretical lowest temperature possible, which occurs when all random motion of molecules has ceased
Acceleration due to gravity The acceleration produced in a body
due to the earth’s attraction is called acceleration due to gravity. It is denoted by the letter g. Its SI unit is m/s². On the surface of the earth, its average value is 9.8m/s². The value of g on the surface of the earth increases in going towards the poles from the equator. The acceleration due to gravity of the earth decreases with altitude and with depth inside the earth. The value of g at the center of the earth is zero.
Acceleration The rate of change of velocity of a moving object is
called its acceleration. The SI units of acceleration are m / s². By
definition, this change in velocity can result from a change in speed, a change in direction, or a combination of changes in speed and direction
Alpha particle The nucleus of a helium atom (two protons and two neutrons) emitted as radiation from a decaying heavy nucleus; also known as an alpha ray
Alternating current An electric current that first moves one direction, then the opposite direction with a regular frequency
Ampere Unit of electric current. It is equivalent to coulomb/sec.
Amplitude (of waves) The maximum displacement of particles of the medium from their mean positions during the propagation of a wave is called the amplitude of the wave.
Amplitude (of an oscillation) The maximum displacement of a body from its mean position during an oscillatory motion is called the amplitude of oscillation.
Angle of incidence Angle of an incident (arriving) ray or particle to a surface; measured from a line perpendicular to the surface (the normal)
Angle of reflection Angle of a reflected ray or particle from a
surface; measured from a line perpendicular to the surface (the
normal)
Atom The smallest unit of an element that can exist alone or in
combination with other elements
Atomic number The number of protons in the nucleus of an atom
Axis The imaginary line about which a planet or other object rotates
Background Radiation Ionizing radiation (alpha, beta, gamma, etc.) from natural sources
Balanced Forces When a number of forces act on a body, and the resultant force is zero, then the forces are said to be resultant
forces.
Barometer An instrument that measures atmospheric pressure,
used in weather forecasting and in determining elevation above sea level
Beta particle High-energy electron emitted as ionizing radiation
from a decaying nucleus; also known as a beta ray
Boiling point The temperature at which a phase change of liquid to gas takes place through boiling. It is the same temperature as the condensation point
Cathode rays Negatively charged particles (electrons) that are
emitted from a negative terminal in an evacuated glass tube
Celsius scale of temperature: In the Celsius scale of temperature,
the ice-point is taken as taken as the lower fixed point (0 deg C )
and the steam-point is taken as the upper fixed point (100 deg C). The interval between the ice point and steam point is divided into 100 equal divisions. Thus, the unit division on this scale is 1degC. This scale was earlier called the centigrade scale. 1 deg C = 9/5 deg F.
Centrifugal force An apparent outward force on an object following a circular path that. This force is a consequence of the third law of motion
Centripetal force The force required to pull an object out of its
natural straight-line path and into a circular path.
Circular Motion The motion of a body along a circular path is called circular motion.
Compression A part of a longitudinal wave in which the density of the particles of the medium is higher than the normal density is
called a compression.
Condensation Where more vapor or gas molecules
are returning to the liquid state than are evaporating
Condensation point the temperature at which a gas or vapor
changes back to a liquid
Conduction The transfer of heat from a region of higher
temperature to a region of lower temperature by increased kinetic energy moving from molecule to molecule
Convection Transfer of heat from a region of higher temperature to
a region of lower temperature by the displacement of high-energy
molecules-for example, the displacement of warmer, less dense air
(higher kinetic energy) by cooler, denser air (lower kinetic energy)
Conventional current Opposite to electron current-that is, considers
an electric current to consist of a drift of positive charges that flow
from the positive terminal to the negative terminal of a battery
Coulomb Unit used to measure quantity of electric charge;
equivalent to the charge resulting from the transfer of 6.24 billion
particles such as the electron
Crest The point of maximum positive displacement on a transverse
wave is called a crest.
Critical angle Limit to the angle of incidence when all light rays are
reflected internally
Decceleration See retardation
Destructive interference The condition in which two waves arriving
at the same point at the same time out of phase add amplitudes to
create zero total disturbance. (also see constructive interference
Diffraction The bending of light around the edge of an opaque
object
Direct current An electrical current that always moves in one
direction
Direct proportion When two variables increase or decrease together
in the same ratio (at the same rate)
Dispersion The effect of spreading colors of light into a spectrum
with a material that has an index of refraction that varies with
wavelength
Displacement The change in the position of an object in a particular
direction is called displacement. Displacement may also be defined
as the shortest distance between the initial and final position of a
moving body. It is a vector quantity.
Distance The actual length of the path traveled by a body
irrespective of the direction is called the distance traveled. It is a
scalar quantity.
Echo A reflected sound that can be distinguished from the original
sound, which usually arrives 0.1 sec or more after the original
sound
Electric circuit Consists of a voltage source that maintains an
electrical potential, a continuous conducting path for a current to
follow, and a device where work is done by the electrical potential;
a switch in the circuit is used to complete or interrupt the
conducting path
Electric current The flow of electric charge electric field force field
produced by an electrical charge
Electric field lines A map of an electric field representing the
direction of the force that a test charge would experience; the
direction of an electric field shown by lines of force
Electric generator A mechanical device that uses wire loops
rotating in a magnetic field to produce electromagnetic induction in
order to generate electricity
Electric potential energy Potential energy due to the position of a
charge near other charges
Electrical conductors Materials that have electrons that are free to
move throughout the material; for example, metals
Electrical energy A form of energy from electromagnetic
interactions; one of five forms of energy-mechanical, chemical,
radiant, electrical, and nuclear
Electrical force A fundamental force that results from the interaction
of electrical charge
Electrical insulators Electrical nonconductors, or materials that
obstruct the flow of electric current
Electrical resistance The property of opposing or reducing electric
current
Electrolyte Water solution of ionic substances that conducts an
electric current
Electromagnet A magnet formed by a solenoid that can be turned
on and off by turning the current on and off
Electromagnetic force One of four fundamental forces; the force of
attraction or repulsion between two charged particles
Electromagnetic induction Process in which current is induced by
moving a loop of wire in a magnetic field or by changing the
magnetic field
Electromagnetic waves The waves which are due to oscillating
electrical and magnetic fields and do not need any material medium
for their propagation are called electromagnetic waves. These
waves can, however, travel through material medium also. Light
waves, radio waves are examples of electromagnetic waves. All
electromagnetic waves travel in vacuum with a speed of 3×10 8
m/s.
Electron current Opposite to conventional current; that is, considers
electric current to consist of a drift of negative charges that flows
from the negative terminal to the positive terminal of a battery
Electron Subatomic particle that has the smallest negative charge
possible and usually found in an orbital of an atom, but gained or
lost when atoms become ions
Electrostatic charge An accumulated electric charge on an object
from a surplus or deficiency of electrons; also called
Energy The capacity of a body to do work is called its energy.
Energy is a scalar quantity. The SI unit of energy is Joule.
Evaporation Process of more molecules leaving a liquid for the
gaseous state than returning from the gas to the liquid. It can occur
at any given temperature from the surface of a liquid. Evaporation
takes place only from the surface of the liquid. Evaporation causes
cooling. Evaporation is faster if the surface of the liquid is large, the
temperature is higher and the surrounding atmosphere does not
contain a large amount of vapor of the liquid.
healthy person is 37 deg C or 98.6 deg F.
First law of motion Every object remains at rest or in a state of
uniform straight-line motion unless acted on by an unbalanced
force
Fluids Matter that has the ability to flow or be poured; the individual
molecules of a fluid are able to move, rolling over or by one another
Force Force is a push or pull which tends to change the state of
rest or of uniform motion , the direction of motion, or the shape and
size of a body. Force is a vector quantity. The SI unit of force is
Newton, denoted by N. One N is the force which when acts on a
body of mass 1 kg produces an acceleration of 1 m/s².
Force of gravitation The force with which two objects attract each
other by virtue of their masses is called the force of gravitation. The
force of attraction acts even if the two objects are not connected to
each other. It is an action-at-a-distance force.
Free fall The motion of a body towards the earth when no other
force except the force of gravity acts on it is called free fall. All
freely falling bodies are weightless.
Freezing point The temperature at which a phase change of liquid
to solid takes place; the same temperature as the melting point for
a given substance
Frequency (of waves) The number of waves produced per second
is called its frequency.
Frequency (of oscillations) The number of oscillations made by an
oscillating body per second is called the frequency.
Friction The force that resists the motion of one surface relative to
another with which it is in contact. The cause of friction is that
surfaces, however smooth they may look to the eye, on the
microscopic scale have many humps and crests. Thus the actual
area of contact is very small indeed, and the consequent very high
pressure leads to local pressure welding of the surface. In motion
the welds are broken and remade continually.
g Symbol representing the acceleration of an object in free fall due
to the force of gravity; its magnitude is 9.80 m/sec^2 (32.0 ft/sec^2)
Gamma ray Very short wavelength electromagnetic radiation
emitted by decaying nuclei
Gases A phase of matter composed of molecules that are relatively
far apart moving freely in a constant, random motion and have
weak cohesive forces acting between them, resulting in the
characteristic indefinite shape and indefinite volume of a gas
compound
Gravitational constant G The constant G which appears in the
equation for Newton’s law of gravitation is called the universal
constant of gravitation or the gravitational constant. Numerically it is
equal to the force of gravitation, which acts between two bodies of
mass 1kg each separated by a distance of 1m. The value of G is
6.67×10-11 Nm²/kg².
Greenhouse effect The process of increasing the temperature of
the lower parts of the atmosphere through redirecting energy back
toward the surface; the absorption and reemission of infrared
radiation by carbon dioxide, water vapor, and a few other gases in
the atmosphere
Ground state Energy state of an atom with electrons at the lowest
energy state possible for that atom
Half-life The time required for one-half of the unstable nuclei in a
radioactive substance to decay into a new element
Heat is a form of energy, which makes a body hot or cold.
Heat is measured by the temperature-effect it produces in any
material body. The SI unit of heat is Joule( J).
Hypothesis A tentative explanation of a phenomenon that is
compatible with the data and provides a framework for
understanding and describing that phenomenon
Ice-point It is the melting point of pure melting ice under 1 atm
pressure. The ice point is taken as the lower fixed point ( 0 deg C or
32 deg F ) for temperature scales.
Incident ray Line representing the direction of motion of incoming
light approaching a
boundary
Index of refraction The ratio of the speed of light in a vacuum to the
speed of light in a material
Inertia The property of matter that causes it to resist any change in
its state of rest or of uniform motion. There are three kinds of
Insulators Materials that are poor conductors of heat-for example,
heat flows slowly through materials with air pockets because the
molecules making up air are far apart; also, materials that are poor
conductors of electricity, for example, glass or wood
Intermolecular forces Forces of interaction between molecules
Internal energy Sum of all the potential energy and all the kinetic
energy of all the molecules of an object
Inverse proportion The relationship in which the value of one
variable increases while the value of the second variable decreases
at the same rate (in the same ratio)
Ionization Process of forming ions from molecules
Ionized An atom or a particle that has a net charge because it has
gained or lost electrons
Isotope Atoms of an element with identical chemical properties but
with different masses; isotopes are atoms of the same element with
different numbers of neutrons
Joule Metric unit used to measure work and energy; can also be
used to measure heat; equivalent to newton-meter
Kelvin scale of temperature On this scale, the ice-point (the lower
fixed point) is taken as 273.15K and the (the upper fixed point) is
taken as 373.15K. The interval between these two points is divided
into 100 equal parts. Each division is equal to 1K.
Kilogram The fundamental unit of mass in the metric system of
measurement
Kinetic Energy Energy possessed by a body by the virtue of its
motion is called kinetic energy. Kinetic energy = 1/2 m v²
Latent heat of vaporization The heat absorbed when one gram of a
substance changes from the liquid phase to the gaseous phase, or
the heat released when one gram of gas changes from the gaseous
phase to the liquid phase
Latent heat of fusion The quantity of heat required to convert one
unit mass of a substance from solid to the liquid state at its melting
point (without any change in its temperature) is called its latent heat
of fusion (L). The SI unit of latent heat of fusion is J kg-1.
Latent heat Refers to the heat hidden in phase changes
Law of Conservation of Energy The change of one form of energy
into another is called transformation of energy. For example, when
a body falls its potential energy is converted to kinetic energy.
Light-year The distance that light travels through empty space in
one year, approximately 9.5 x 10^11 km
Liquids A phase of matter composed of molecules that have
interactions stronger than those found in a gas but not strong
enough to keep the molecules near the equilibrium positions of a
solid, resulting in the characteristic definite volume but indefinite
shape of a liquid
Liter A metric system unit of volume, usually used for liquids
Longitudinal waves The wave in which the particles of the medium
oscillate along the direction along the direction of propagation of
wave is called the longitudinal wave. Sound waves are longitudinal
waves.
Loudness A subjective interpretation of a sound that is related to
the energy of the vibrating source, related to the condition of the
transmitting medium, and related to the distance involved
Magnetic field Model used to describe how magnetic forces on
moving charges act at a distance
Magnetic poles The ends, or sides, of a magnet about which the
force of magnetic attraction seems to be concentrated
Magnitude The size of a measurement of a vector; scalar quantities
that consist of a number and unit only, no direction, for example
Mass number The sum of the number of protons and neutrons in a
nucleus defines the mass number of an atom; used to identify
isotopes; for example, Uranium 238
Mass The quantity of matter contained in a body is called its mass.
The SI unit of mass is kg. The mass of a body remains the same
everywhere. It is a measure of inertia, which means a resistance to
a change of motion
Matter Anything that occupies space and has mass
Mechanical energy The form of energy associated with machines,
objects in motion, and objects having potential energy that results
from gravity
Melting point The temperature at which a phase change of solid to
liquid takes place; the same temperature as the freezing point for a
given substance
Metal Matter having the physical properties of conductivity,
malleability, ductility, and luster
Meter The fundamental metric unit of length
Millibar A measure of atmospheric pressure equivalent to 1.000
dynes per cm ^2
Mixture Matter made of unlike parts that have a variable
composition and can be separated into their component parts by
physical means
Model A mental or physical representation of something that cannot
be observed directly that is usually used as an aid to understanding
Mole An amount of a substance that contains Avogadro’s number
of atoms, ions, molecules, or any other chemical unit; a mole is
thus 6.02 x 10^23 atoms, ions, or other chemical units
Momentum Momentum is considered to be a measure of the
quantity of motion in a body. The momentum of a body is defined
as the product of its mass and velocity. Its SI units are kg m /s.
Negative electric charge One of the two types of electric charge;
repels other negative charges and attracts positive charges
Negative ion Atom or particle that has a surplus, or imbalance, of
electrons and, thus, a negative charge
Newton A unit of force defined as kg.m/sec^2; that is, a 1 Newton
force is needed to accelerate a 1 kg mass 1 m/sec^2
Newton’s first law of motion A body continues in a state of rest or of
uniform motion in a straight line unless it is acted upon by an
external (unbalanced) force.
Newton’s second law of motion The rate of change of momentum is
equal to the force applied OR the force acting on a body is directly
proportional to the product of its mass and acceleration produced
by the force in the body.
Newton’s third law of motion To every action there is an equal and
opposite reaction. The action and reaction act on two different
bodies simultaneously.
Non Uniform Acceleration When the velocity of a body increases by
unequal amounts in equal intervals of time, it is said to have nonuniform
acceleration.
Non Uniform Speed When a body travels unequal distances in
equal intervals of time then it is said to have non-uniform speed.
Non Uniform Velocity When a body covers unequal distances in
equal intervals of time in a particular direction, or when it covers
equal distances in equal intervals but changes its direction it is said
to have non uniform velocity.
Normal A line perpendicular to the surface of a boundary
Nuclear energy The form of energy from reactions involving the
nucleus, the innermost part of an atom
Nuclear fission Nuclear reaction of splitting a massive nucleus into
more stable, less massive nuclei with an accompanying release of
energy
Nuclear force One of four fundamental forces, a strong force of
attraction that operates over very short distances between
subatomic particles; this force overcomes the electric repulsion of
protons in a nucleus and binds the nucleus
together
Nuclear fusion Nuclear reaction of low mass nuclei fusing together
to form more stable and more massive nuclei with an
accompanying release of energy
Nuclear reactor Steel vessel in which a controlled chain reaction of
fissionable materials releases energy
Nucleons Name used to refer to both the protons and neutrons in
the nucleus of an atom
Nucleus Tiny, relatively massive and positively charged center of
an atom containing protons and neutrons; the small, dense center
of an atom numerical constant a constant without units; a number
Ohm Unit of resistance; equivalent to volts/amps
Ohm’s law The electric potential difference is directly proportional to
the product of the current times the resistance
Physical change A change of the state of a substance but not the
identity of the substance pitch the frequency of a sound wave
Positive electric charge One of the two types of electric charge;
repels other positive charges and attracts negative charges
Positive ion Atom or particle that has a net positive charge due to
an electron or electrons being torn away
Potential Energy Energy possessed by a body by the virtue of its
position or configuration is called potential energy. There are two
types of potential energies, gravitational and elastic. The potential
energy of a body by virtue of its height from the ground is called its
gravitational potential energy. The potential energy of a body by
virtue of its configuration (shape) is called its elastic potential
energy.
Power The rate of doing work is called power. Power is a scalar
quantity. The SI unit of power is Watt ( 1 W = 1 J/sec)
Pressure Defined as force per unit area; for example, pounds per
square inch (lb/in^2)
Primary coil Part of a transformer; a coil of wire that is connected to
a source of alternating
current
Pulse A wave of short duration confined to a small portion of the
medium at any given time is called a pulse. A pulse is also called a
wave pulse.
Radiation The transfer of heat from a region of higher temperature
to a region of lower temperature by greater emission of radiant
energy from the region of higher temperature
Radioactive decay The natural spontaneous disintegration or
decomposition of a nucleus
Radioactivity Spontaneous emission of particles or energy from an
atomic nucleus as it disintegrates
Rarefaction A part of a longitudinal wave in which the density of the
particles of the medium is less than the normal density is called a
rarefaction.
Real image An image generated by a lens or mirror that can be
projected onto a screen
Reflected ray A line representing direction of motion of light
reflected from a boundary
Reflection The change when light, sound, or other waves bounce
backwards off a boundary
Refraction A change in the direction of travel of light, sound, or
other waves crossing a boundary
Resultant Force A single force, which acts on a body to produce the
same effect in it as, done by all other forces collectively, is called
the resultant force.
Retardation Negative acceleration is called retardation. In
retardation the velocity of a body decreases with time.
Saturated solution The apparent limit to dissolving a given solid in a
specified amount of water at a given temperature; a state of
equilibrium that exists between dissolving solute and solute coming
out of solution
Scalar Quantity A physical quantity, which is described completely
by its magnitude, is called a scalar quantity.
Second law of motion The acceleration of an object is directly
proportional to the net force acting on that object and inversely
proportional to the mass of the object
Secondary coil Part of a transformer, a coil of wire in which the
voltage of the original alternating current in the primary coil is
stepped up or down by way of electromagnetic induction
Simple Pendulum A heavy point mass (actually a small metallic
ball), suspended by a light inextensible string from a frictionless
rigid support is called a simple pendulum. A simple pendulum is a
simple machine based on the effect of gravity.
Solenoid A cylindrical coil of wire that becomes electromagnetic
when a current runs through it
Solids- A phase of matter with molecules that remain close to fixed
equilibrium positions due to strong interactions between the
molecules, resulting in the characteristic definite shape and definite
volume of a solid
Specific heat -Each substance has its own specific heat, which is
defined as the amount of energy (or heat) needed to increase the
temperature of one gram of a substance one degree Celsius
Speed The distance traveled by a body in one unit of time is called
its speed. If a body covers distance s in time t then its speed is
given by s / t. It is a scalar quantity and its SI unit’s are m / s.
Steam-point It is the temperature of steam over pure boiling water
under 1 atm pressure. The steam point is taken as the upper fixed
point (100 deg C or 212 deg F) for temperature scales.
Temperature It is a numerical measure of hotness or coldness of a
body. According to the molecular model, it is a measure of the
average kinetic energy of the molecules of the body. Heat flows
from a body at higher temperature to a body at lower temperature.
Tensional stress The opposite of compressional stress; occurs
when one part of a plate moves away from another part that does
not move
Thermal Capacity The quantity of heat required to raise the
temperature of the whole body by one degree (1K or 1deg C) is
called its thermal capacity.
Thermal Expansion The increase in the size of an object on heating
is called thermal expansion.
Thermometer It is a device used for numerical measurement of
temperature. The commonly used thermometer is mercury
thermometer.
Third law of motion Whenever two objects interact, the force
exerted on one object is equal in size and opposite in direction to
the force exerted on the other object; forces always occur in
matched pairs that are equal and opposite
Time Period (of a wave) The time taken by a wave to travel through
a distance equal to its wavelength is called its time period. It is
denoted by T. Time period of a wave=1/frequency of the wave.
Time Period (of an oscillation) The time taken to complete one
oscillation is called the time period of an oscillation. The time period
of a pendulum does not depend upon the mass of the bob and
amplitude of oscillation. The time period of a pendulum is directly
proportional to the square root of the length and inversely
proportional to the square root of the acceleration due to gravity.
Total internal reflection Condition where all light is reflected back
from a boundary between materials; occurs when light arrives at a
boundary at the critical angle or beyond
Transverse waves A wave in which the particles of the medium
oscillate in a direction perpendicular of the direction of propagation
of wave is called the transverse wave. Water waves, light waves
and radio waves are examples of transverse waves.
Ultrasonic Sound waves too high in frequency to be heard by the
human ear; frequencies above 20,000Hz
Unbalanced forces When a number of forces act on a body and the
resultant force is not zero, then the forces are said to be
unbalanced.
Uniform Acceleration When the velocity of a body increases by
equal amounts in equal intervals of time it is said to have uniform
acceleration.
Uniform Circular Motion The motion of an object in a circular path
with uniform speed is called uniform circular motion. Uniform
circular motion is accelerated motion.
Uniform Speed When a body travels equal distances in equal
intervals of time then it is said to have uniform speed.
Uniform Velocity When a body travels along a straight line in
particular direction and covers equal distances in equal intervals of
time it is said to have uniform velocity.
Vapour The gaseous state of a substance that is normally in the
liquid state
Vector Quantity A quantity, which needs both magnitude and
direction to describe it, is called a vector quantity. Such a physical
quantity should also follow the vector law of addition.
Velocity Distance traveled by a body in a particular direction per
unit time is called its velocity. It can also be defined as the
displacement of the body per unit time. It is a vector quantity. The
SI units of velocity are m / s.
Vibration A back and forth motion that repeats itself
Virtual image An image where light rays appear to originate from a
mirror or lens; this image cannot be projected on a screen
Volt Unit of potential difference equivalent to joules/coulomb
Voltage drop The electric potential difference across a resistor or
other part of a circuit that consumes power
Watt Metric unit for power; equivalent to joule/sec
Wave motion The movement of a disturbance produced in one part
of a medium to another involving the transfer of energy but not the
transfer of matter is called wave motion.
Wave period The time required for two successive crests or other
successive parts of the wave to pass a given point
Wave velocity The distance traveled by a wave in one second is
called the wave velocity. The wave velocity of a wave depends
upon the nature of the medium through which it passes.
Wave (mechanical) A periodic disturbance produced in a material
medium due to the vibratory motion of the particles of the medium
is called a wave.
Wave A disturbance or oscillation that moves through a medium
Wavelength The distance between the two nearest points on a
wave, which are in the same phase, is called the wavelength of the
wave. The distance between two adjacent crests or two adjacent
troughs is called its wavelength.
Weight The force with which a body is attracted towards the center
of the earth is called its weight. The SI unit of weight is N. The
gravitational units of weight are kg-wt and g-wt. The weight of a
body of mass m is given by mg. Its value will depend upon the
value of g at that place. The weight of a body is measured with a
spring balance.
Work Work is done when a force acting on a body displaces it.
Work is a scalar quantity. The SI unit for work is Joule
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